Transmission control system



Jan. 25, 1949.

A. c. DlCKiESON TRANSMISSION CONTROL SYSTEM Filed June 1, 1946 f I G. l maven 0y M F4 r4 0- 7 F AMP l PASS l 2 2 g F/PWUE/VCY C FfitWVE/VC) MANUAL 0R AUTOMATIC ADJUSTMENT PASS CI'CZ'VZ MOD. LFYI AMP mfqwmcy v2 F; A,

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E] INPUT C INPUTA b X g 1: REPRESENTS ODD-ORDER (FOR EXAMPLE COPPER oxloE) /N l/ENTOR A. C. DICK/550M ATTORNEY Patented Jan. 25,1949

TRANSMISSION CONTROL SYSTEM Alton C. Dickieson, Mountain Lakes, N. ,J.,-as ,l

Signor to Bell Telephone Laboratories, Encore. I

' porated, New York, N.

York

Y., a corporation off-New Application June 1, 1946, Serial No. 673,874

. v 1 f This invention relates systems and modulating systems. V

. 1 An object of theinvention is to so control the gain of two or more amplifiers or transmission paths or channels that their gains track, or in other words, the gain changes are accurately alike in allchannels. l

In conventional automatic gain control systems using variable grid bias, tracking requires matching tube characteristics over a wide range, which is not commercially practical. Various pilot frequency methods are used, involving passing control frequencies through the amplifiers.

' An object of theinvention is to obtain gain tracking without dependence on matching active elements or on passing pilot tones through them. Inv accordance with the invention this may be accomplished by applying .two' signals to two modn ulators, respectively, applying to each modulator the same two carrier waves, one of which has its amplitude varied and the other-of which has its amplitude always'exceeding said varied amplitude and the maximum useful amplitude of the signal applied tothe modulator, and selecting from the output of each modulator a modulation product which varies in magnitude directly as the applied signal and the 'amplitudefof the applied variable carrier wave separately.

The modulators preferably are like, passive, odd 'order modulators. For example, each maycom prise twelve odd order modulatorelements in the linear configuration of the edges of a cube, with the four pairs of points at the ends of the diagonals of the cube all conjugate to each other. Such a modulator is one aspect of the invention.

Other objects and features of the invention will be apparent irom the followingdescription and claims.

F ig. 1 shows a circuit for maintaining gain tracking in amplifiers in accordance with the invention; and

Fig. 2 shows a modulator circuit, in accordance with the invention, which may be used in the circuit of Fig. 1.

In Fig. 1, S1 is a source of a signal voltage wave of frequency V1, S2 is a source of a signal voltage wave of frequency V2, 0 1 is a source of a carrier voltage wave of frequency C1, and O2 is a source of a carrier voltage wave of frequenc C2 whose amplitude can be varied by adjustment of a con- 6 Claims. (01. 179-1715) to transmission control troLG symbolically indicated as avariable resistance in the ,C z s lpply, Though frequencies V1 and V2 are not necessarily equal, in manyapplications of th invention-they will be equal and the waves of frequencies V1 and V2 will be subject to difference in phase, for example The symbol V isused herein as a general symbol for V1 and V2. The waves of frequencies V1, Grand C2 are intermodulated in modulator Mifas indicated'in Fig.1: Similarly, the waves of frequencies V2, C1 and C2 are intermodulated .in modulator M2. The

, wave of 1 frequency- C1 is of fixed amplitude, larger than the maximum usable magnitude of the wave of frequency V. The'wave. offrequencyCz is of variable amplitude always smalle'r' than theamplitude of the wave of frequency C1. 1

'Thus, in the case of'each of the modulators M1 and M2, .theinputwaves are of frequencies V, 01 and C2. .The output frequency used is .selected, by filter Flor F5, from the general't'e'rm iC'iiCziV. In the .caseshown li'n' Fig. l, the choice isCi Czel/T. Thewavewof the. selected frequency, either C1" C V or other, choice from the generalterm :tCfii-Cii'll varies in amplitude directly as the amplitudes, of the, waves of free quen'cies V and Czseparately, and is independent of the amplitude or theiwav'eof 'frequenc ,;.C1. 'The selected wave may be amplif ed in amplifier A1 or A2. Modulatorcharacteristics do not .,affect tracking .since the input jwave fo'f largest 'magnitude (the wave of'frequencyfCi) is keptl'fix'ed in amplitude- With the wave'offirequency C1large in ame 'plitud'e, and the magnitude of the wave selected from the modulator output therefore proportional to both thejmagriitudeof the :wave of frequency C2 and the magnitude'pf the ave of frequency V, the wave of "frequency V C2 can be varied inam'plitude tofvaryj the modulator loss decibel for decibel. So long asthe magnitude of thejwave of frequency 01 has at leastj'a value approximately between '6' and '10 decibels greater than the magnitudes of the waves of frequencies C2 and V, it is known from experience that the loss Varies accurately as either of these other inputs.

The modulators M1 and M2 are in the input circuits of the amplifiers A1 and A2, respectively. Thus, the amplifiers are controlled in gain by adjustment of the common control G in the C2 supply. This common adjustment can be controlled by any desired means, as for example manual, time controlled (TVG), reverberation controlled (RCG), or automatic volume control (AVC) means, the control G being intended as symbolic of any such means.

Though the desired term 01-02-1 varies in magnitude as C2, there are other modulation products involving only C1 and V which do not change at all as C: is varied in amplitude. These canbe discriminated against by frequency selectivity, as by proper choice of the C1 and C2. frequencies, or" .by balance of rectifier elements. Since the term used is odd order, it is desirable to use an odd order modulator to achieve the most, from balances. J

Fig. 2 shows an odd order modulator :system' comprising twelve odd order, two-terminal modu lating elements interconnected in the manner of the twelve edges of a cube. Each element may be a Thyrite element or may be formedof two rectifiers, as for example copperoxide rectifiers, connected in parallel and poled oppositely. The four pairs of opposite points AA, BB, CC and DD 'to the exclusion of the other products of said -signal wave for modulating said carrier wave in are all conjugate to each other, from the symmetry of the system. If three input waves of frequencies-A, B, andQrespectiVely, are applied as shown, it can be demonstrated that the products of .the class iAniBozL-C'o all appear at the fourth 'pairof pointsDD Ao meaning the term involving odd "orders of thefrequency A, etc), and no other terms appear at this outlet except by unbalance. 7 especially well suited for-use in the system of Fig. 1.

What is clalmed isz 1. The method which comprises intermodulating a first signal voltage, a first carrier voltage of one frequency and of fixed amplitude larger than the maximum usable value of said signal voltage, and a second carrier voltage of another frequency and of variable amplitude always smaller than said fixed amplitude, separately intermoclulating a second signal voltage, saidfirst carrier voltage and said second carrier voltage, said "first amplitude exceeding the maximum usable value of said second signal voltage, selecting from products of. said first modulation one which varies in magnitude directly as each of said 'first signal and second carrier voltages I separately, and selectingfrom products of said lators signal waves of frequencies V1 and. V2, respectively, means for supplying to each of said,

Thus, this modulator is said other device, each of said devices being adapted to vary its modulator gain linearly by the same factor with variation of the amplitude of said'carrier wave;

4. An odd order modulator comprising twelve like, two-terminal odd order modulating elements interconnected in the manner of the twelve edges of a cube, with the four pairs of points at the ends of the diagonals of the cube all conjugate to each other.

5. An odd order modulating system comprising twelve like, two-terminalodd order modulating elements interconnected inthe'manner. of the twelve edges of a cube, with'the four pairs of 7 points at the ends of the diagonals of the cube all conjugate to each other, means for applying to three of said pairs three waves of different frequencies A, B and C, respectively, and means for deriving from the fourth of said pairs modu-. lation products of the class 'iAoiBoi-Coto the exclusion of all other terms.

6. A system comprising two like modulators, each including twelve two-terminallodd order modulating elements interconnected in the manner of the twelve edges of a cube with the four pairs of points at the ends of the diagonals of the cube all conjugate to each other, means for applying a signal voltage of frequency V1, a carrier voltage of frequency C1 and a carrier voltage of another frequency C2 to three of said pairs, respectively, of one of said modulators, means for applying asignal voltage of frequency V2, said carrier voltage of frequency Crand said carrier voltage of frequency C2 to three of said pairs, respectively, oflsaid other modulator, and means forvarying the amplitude of said carrier voltage of frequency C2, said carriervoltage of modulators" a carrier wave of frequencyCz.

said other. waves supplied to said modulators,

means connected to one of said modulators for 6 deriving therefrom a wave whose frequency is one of the eight in the general term i'cli czivi frequency C1 having a fixed amplitude always larger than the amplitude of the carrier voltage of frequency V2 and theimaximum usable magnitude of said signal voltages, r f V ALTON C. DICKIESON.

REFERENCES CITED The, following references are of record in the file of this patent:

'UNITED STATES PATENTS Peterson 'July 8, 1941 

